Rule Item: how to check if it has to be re-run?

Question

In my case, Rule has to be invoked upon environment changes (svn revision of working directory) instead of changes of input files. So, depending on alwaysRun, my rule is invoked either never (failing build) or always (forcing dependers to be rebuilt).

What I need is either:

a way to check if Rule has to be run or not
a way to cache rule output somehow, for dependers only to be rebuilt when necessary

score 1 · Accepted Answer · answered Oct 12 '17 at 08:56

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Rules and Commands are re-run not only due to input changes, but also if properties used in them change. So in your case, you will want to define a property that corresponds to the svn repository state and refer to it in your rule and/or command. Then the re-execution will happen if and only if it is necessary. Note that in qbs 1.10, such a property is provided automatically via the vcs module: http://doc-snapshots.qt.io/qbs/vcs-module.html

answered Oct 12 '17 at 08:56

Christian Kandeler

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am I correct, that properties can only be changed at evaluation, but not build time? – Andrei R. Oct 12 '17 at 11:16
Yes, but re-evaluation will be done on an as-needed basis when re-building. – Christian Kandeler Oct 13 '17 at 08:05
can you suggest how exactly re-evaluation prior to build step can be achieved? Forcing execution of all probes is not an option – Andrei R. Oct 13 '17 at 08:50
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A Probe is re-run if one of its properties changes. So having a Probe property that uses File.lastModified() on a relevant svn file such as wc.db should do the trick. – Christian Kandeler Oct 13 '17 at 12:45

Rule Item: how to check if it has to be re-run?

1 Answers1